(a) Field of the Invention
The present invention relates to a method for preparing 2-(2-hydroxyphenyl)-2H-benzotriazole, in which 2-(2-hydroxyphenyl)-2H-benzotriazole of formula (I) below can be prepared in a high yield and in an economical way.
(b) Description of the Related Art 
wherein X is halogen or hydrogen; R is hydrogen, C1-C12 alkyl, C5-C8 cycloalkyl, phenyl or phenyl-(C1-C 4) alkyl; and Rxe2x80x2 is C1-C12 alkyl, C5-C8 cycloalkyl, phenyl, or phenyl-(C1-C4) alkyl.
Benzotriazole compounds are known in the art as ultraviolet absorbing agents useful for protection of organic polymeric substances from deterioration by ultraviolet irradiation. In general, various methods are known to obtain the benzotriazole by reducing a compound of formula (II) used as a starting reagent via an intermediate product of formula (III). 
wherein, X is halogen or hydrogen; R is hydrogen C1-C12 alkyl, C5-C8 cycloalkyl, phenyl or phenyl-(C1-C4) alkyl; and Rxe2x80x2 is C1-C12 alkyl, C5-C8 cycloalkyl, phenyl, or phenyl-(C1-C4) alkyl.
Among the known processes, a method in which hydrazine is used as a reducing agent has an advantage in that it allows the reaction to be carried out under atmospheric pressure (U.S. Pat. No. 4,001,266, Ger. Often. DE 2,454,889, Fr Demande FR 2,292,708), but it also has disadvantages in that expensive ethers such as diethylene glycol diethyl or dimethyl ether are used as solvents, and that the reaction temperature is at least 100xc2x0 C. (in the Examples of the present invention; at least 130xc2x0 C.), thereby a side-reaction takes place to form large amounts of byproducts. Moreover, reaction time is prolonged in order to distill off water that is present in the reagents, and during distillation by heating of the reactants, there is even a potential danger of explosion due to the property of ether as a solvent that it can easily produce peroxid compounds.
The intermediate product that is denoted by the formula (III) can be synthesized by a reaction of a derivative having the formula (II) with zinc powder in the presence of low alcohol or water (Japan Kokai JP 53,063,379), and in such a case, since an excessive amount of zinc (4 equivalents) and alkali metals (4 equivalents) are used, post treatment of large amounts of zinc product is required and cost of waste treatment is increased for the neutralization of the excessive amount of alkali metals.
Alternatively, there is an example of using hydrazine and zinc as reducing agents and an alcohol as a solvent, but, in this case, for the preparation of an N-oxide compound having the formula (III), the solvent has to be changed to chlorobenzene after crystallization and filtration. Consequently, there are drawbacks in that a large numbers of equipments are needed and the complicated process causes an extension of the processing period, and furthermore, there can be a product loss through the filtrate during filtration as well as other problems such as additional cost for the solvent recovery.
In consideration of the abovementioned problems, it is an object of the present invention to provide a method for preparing 2-(2-hydroxyphenyl)-2H-benzotriazole of the formula (I) above in an economical way and with a high yield by simplifying solvents used.
In order to achieve the object of the present invention, there is provided a method for preparing 2-(2-hydroxyphenyl)-2H-benzotriazole of formula (I) below, comprising steps of:
a) performing a first reduction in which hydrazine hydrate is added to a compound of formula (II) below with or without a phase transition catalyst in the presence of solvents which include a nonpolar solvent, water, and an alkaline compound, thereby preparing a compound of formula (III) below; and
b) performing a second reduction in which water is added to the compound of formula (III) prepared in step a), and then zinc powder and sulfuric acid are added thereto with or without the phase transition catalyst: 
wherein, X is halogen or hydrogen; R is hydrogen, C1-C12 alkyl, C5-C8 cycloalkyl, phenyl, or phenyl-C1-C4 alkyl; and Rxe2x80x2 is C1-C12 alkyl, C5-C8 cycloalkyl, phenyl, or phenyl-C1-C4 alkyl.